1. Field of the Invention
The present invention generally relates to fluid fan clutch devices of a type in which fan rotation for engine cooling in an automobile or the like is controlled by following a change in external ambient temperature or a change in rotation and, in more detail, relates to a temperature-sensitive fluid fan clutch device for promoting speedup in reaction of fan rotation and inhibition of cold “drag”.
2. Description of the Related Art
Conventionally, as a fan clutch device which controls fan rotation for engine cooling in an automobile or the like to supply a controlled cooling blast amount to an engine, there are a temperature-sensitive type, an external control type, and so forth. The temperature-sensitive type includes one in which: the inside of a sealed housing formed of a case and a cover is partitioned by a partition plate having an oil supply adjustment hole into an oil reservoir chamber and a torque transmission chamber having a drive disk built therein; a dam is formed on part of an inner peripheral wall surface of the sealed housing facing an outer circumferential wall of the drive disk where oil is collected and accumulated in rotation; an oil circulating flow passage (oil collection duct) contiguous to the dam is provided between the torque transmission chamber and the oil reservoir chamber; and an oil supply valve member is provided therein, the oil supply valve member opening the supply adjustment hole of the partition plate when external ambient temperature exceeds a set value and closing the supply adjustment hole of the partition plate when the temperature is equal to or lower than the set value, wherein an effective contact area of oil in a torque transmission gap provided between the drive disk and a wall surface of the sealed housing near outside facing the drive disk is increased and decreased to control rotation torque transmission from the drive side to the sealed housing on the driven side. The fan clutch device of this type generally takes a scheme of detecting atmospheric temperature by a bimetal of a strap type or spiral type and adjusting opening of the oil supply adjustment hole in accordance with this detection value (refer to Japanese Patent Application Laid-Open No. 2000-74098).
The conventional temperature-sensitive fluid fan clutch device has a mechanism in which: by oil supplied from the oil reservoir chamber via the oil supply adjustment hole of the partition plate to the torque transmission chamber, drive torque of the drive disk is transmitted to the sealed housing (case) to cause a fan attached to the sealed housing to rotate; and by a dam formed on part of the inner periphery on a sealed housing side facing the outer circumference of the drive disk, oil is collected by the oil circulating flow passage (oil collection duct) leading to the oil reservoir chamber from a torque transmission chamber side.
However, in the case of this scheme of collecting oil through the oil circulating flow passage (oil collection duct) by the dam formed on part of the inner periphery on the sealed housing side facing the outer circumference of the drive disk, since the collection capability of the dam is relatively low at low input rotation speed, in particular, initially at low temperature, the oil collection amount is insufficient and causes an undesired rotation of the fan caused by oil remaining in the torque transmission chamber. This phenomenon is referred to herein as a “drag” or “cold pump out” phenomenon, and creates an increase of hysteresis action that means a difference in operating temperature between temperature rising characteristics and temperature falling characteristics. In other words, it is meant that large hysteresis action means low collection capability of the dam and, with this dam's insufficient collection capability, oil remaining in the torque transmission chamber causes a “drag” phenomenon. That is, the conventional temperature-sensitive fluid fan clutch device has not achieved high reaction (reduction in hysteresis action) from an ON (activated) state to an OFF (non-activated) state, and the “drag” phenomenon when it is cold cannot be inhibited. From these, the device has a problem that a fan power loss is large and reduction in fuel consumption is not promoted.
The present invention was made to solve the above problem, and is to provide a temperature-sensitive fluid fan clutch device in which the numbers of dams and oil circulating flow passages located at the outer periphery of the drive disk is increased to improve oil collection power, and high reaction from an ON state to an OFF state (reduction in hysteresis action) and inhibition of a “drag” phenomenon occurred when it is cold are promoted, and thereby reduction in fan power loss and reduction in fuel consumption can be achieved.